1. Field of the Invention
This invention relates to a composite implant member adapted for orthopedic, dental and cerebral surgery spheres that is not only used as an endosseous implant member for dental treatment but also used for the restoration of broken, damaged or defective bone structures by implanting the composite implant member both in a hard tissue and in a soft tissue of a living body.
2. Prior Art
The conventional type endosseous implant members as for dental treatment which are made generally of cobalt chromic alloy, titanium, titanium alloy, occasionally of platinum, platinum alloy, gold, gold alloy or stainless alloy are widely used, and the members are of such construction that a channel or hole is formed in the jaw bone, a rod-shaped or plate-shaped implant is embedded therein, and a rod-shaped post portion is caused to project from the rod-shaped or plate-shaped implant which is embedded in the bone and to extend beyond the bony tissue (soft tissue) so as to permit the mounting of an upper structure on the post portion. The portion of the implant to be embedded in the bone is formed with numerous grooves and dents and projections so as to increase an area of contact with the bone to provide stronger fixation to the bone and disperse stress. A multiplicity of vent-holes are formed in the case of the plate-shaped implant member.
In the case of a metal implant member, it is possible to bend the plate-shaped or rod-shaped metal implant in agreement with the channel and hole formed in the bone so as to provide strong initial fixation in time of implanting by making use of the characteristic properties of the metal implant. Accordingly, it is comparatively easy to deal with (modify) the metal implant. But that portion of the implant projecting outside the bone is of such construction that the metal comes in direct contact with the gum. Because the gum reacts with the metal to turn the metal blackish gray, the implant comes to be unaesthetic by lack of color harmony. In addition, because of poor compatibility of the gum with the metal, the gum portion is liable to be absorbed and inflame and makes the bone infected with various germs. Such are some of the disadvantages inherent in the conventional metal type implant member.
In recent years, an artificial dental root of ceramic and particularly that of singlecrystalline or polycrystalline alumina ceramics has come to be widely used. In the artificial dental root of the type described, there are noticed two types according to which one is that the portion of the dental root to be embedded in the bone is made of a plate-shaped metal similar to the metal implant member while the other is a dental root fixed by forming threads in the jaw bone and screwing the implant into the threaded jaw bone. It is devised to improve fixation of the implant to the bone by increasing a surface area by making thread-shaped the portion of the implant embedded in the bone or by forming holes in the portion. But formation of a groove or dents and projections raises a problem such as a great reduction in the strength of the implant and breakage of the implant. Accordingly, the artificial dental root of the type still leaves much to be improved in that it is made larger in thickness than the metal implant and made smooth in surface, resulting in smaller fixability.
Furthermore, the implant of the ceramic type has the disadvantage that also in the initial fixation of the implant, the channel to be formed in the bone must be brought into exact agreement with the implant and that the implant cannot be modified in its form as opposed to that of the metal type. But the ceramic implant is constructed such that the portion of the implant which projects outward beyond the bone makes direct contact with the gum, and in this respect the ceramic implant and the metal implant are the same. In the case of the ceramic implant and particularly in the case of a singlecrystalline alumina ceramic implant, the implant, because of its colorless transparency, does not spoil the beautiful pink color of the gum and is very pleasing in appearance. In addition thereto, the ceramic implant is highly compatible with the gum, so that the gum adheres firmly to the implant and provides perfect sealing between the oral cavity and the living body (jaw bone), preventing an infective agent due to various germs invading the jaw bone.
Furthermore, that metallic implant portion which is embedded in the bone is comparatively easy to handle and accordingly, it provides strong fixation, but it poses a problem at the portion at which it extends beyond the jaw bone, namely at the portion at which it contacts the gum. On the other hand, the ceramic implant is free from any problems at the portion wherein it comes into contact with the gum outside the jaw bone, but it has the disadvantage that the portion of the implant which enters the bone becomes larger in thickness than the metal implant and is impossible of bending and cutting work. In short, the ceramic implant is difficult to handle and particularly leaves much to be discussed in point of initial fixing strength.
An implant member for orthopedic surgery is widely used as for surgical external fixation wherein a broken bone is externally fixed and held and wherein the broken bone area is fixed by an external surgical fixator. In having recourse to this means, it is contemplated to screw a long metal threaded pin through the skin into the bone and to fix the pin outside the bone to reunite the broken bone. In this case also, it poses an important problem that infection is often caused by inflammation occurring at a portion outside the bone, especially at the contacting portion between the soft tissue and the metal pin.